U.S. patent number 7,309,556 [Application Number 11/083,934] was granted by the patent office on 2007-12-18 for black toner and developer.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Thomas C. Dombroski, Deepak R. Maniar, Maria N. V. Mc Dougall, Rachael L. Mc Grath, Mary L. Mc Stravick, Paul W. Morehouse, Jr., Jackie Parker, Christopher M. Pattison, Shigang Qui, Mary B. Schlitzer, Vladislav Skorokhod, Michael D. Thompson, Richard P. N. Veregin.
United States Patent |
7,309,556 |
Mc Dougall , et al. |
December 18, 2007 |
**Please see images for:
( Certificate of Correction ) ** |
Black toner and developer
Abstract
A developer includes black toner particles and carrier
particles, the black toner particles including at least one binder,
at least one black colorant and one or more external additives,
wherein the toner particles comprise from about 7 to about 15 pph
of the developer, and wherein the toner particles exhibit a
triboelectric charge of from about -25 to about -50 .mu.C/g at
toner particle concentrations of about 7 to about 15 pph of the
developer. The developer is ideally suited for use in a high speed
(greater than 100 prints per minute) semiconductive magnetic brush
development apparatus. Preferably, the black toner particles
include a styrene acrylate binder, and the external additives
include from about 1.3 to about 2.1% by weight of the toner
particles of a first silica having an average particle size of from
about 35 to about 45 nm, from about 0.5 to about 1.0% by weight of
the toner particles of a second silica having an average particle
size of from about 135 to about 160 nm, and from about 0.2 to about
0.5% by weight of the toner particles of a titania having an
average particle size of from about 35 to about 45 nm, with an
external additive toner surface area coverage of from about 25 to
about 45%.
Inventors: |
Mc Dougall; Maria N. V.
(Burlington, CA), Veregin; Richard P. N.
(Mississauga, CA), Skorokhod; Vladislav (Mississauga,
CA), Mc Stravick; Mary L. (Fairport, NY), Maniar;
Deepak R. (Webster, NY), Morehouse, Jr.; Paul W.
(Webster, NY), Mc Grath; Rachael L. (Churchville, NY),
Parker; Jackie (Mississauga, CA), Qui; Shigang
(Toronto, CA), Schlitzer; Mary B. (Rochester, NY),
Thompson; Michael D. (Rochester, NY), Pattison; Christopher
M. (Rochester, NY), Dombroski; Thomas C. (Rochester,
NY) |
Assignee: |
Xerox Corporation (Norwalk,
CT)
|
Family
ID: |
35239814 |
Appl.
No.: |
11/083,934 |
Filed: |
March 21, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050250031 A1 |
Nov 10, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10839293 |
May 6, 2004 |
7157200 |
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Current U.S.
Class: |
430/108.6;
430/108.7; 430/111.41; 399/267 |
Current CPC
Class: |
G03G
9/09725 (20130101); G03G 9/08708 (20130101); G03G
9/09708 (20130101); G03G 9/1132 (20130101); G03G
9/0823 (20130101); G03G 9/08782 (20130101) |
Current International
Class: |
G03G
9/087 (20060101) |
Field of
Search: |
;430/108.6,109.3,108.7,111.41 ;399/267 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goodrow; John L
Attorney, Agent or Firm: Oliff & Berridge PLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part application of U.S.
application Ser. No. 10/839,293 filed May 6, 2004, now U.S. Pat.
No. 7,157,200 which application is incorporated by reference herein
in its entirety.
Claims
What is claimed is:
1. A developer comprising black toner particles and carrier
particles, wherein the black toner particles comprise at least one
binder, at least one black colorant and one or more external
additives, wherein the toner particles comprise from about 7 to
about 15 pph by weight of the developer, and wherein the toner
particles exhibit a triboelectric charge of from about -25 to about
-50 .mu.C/g at toner particle concentrations of about 7 to about 15
pph by weight of the developer.
2. The developer according to claim 1, wherein the toner particles
include from about 6 to about 10% by weight of the black
colorant.
3. The developer according to claim 1, wherein the developer
provides a solid area image density of from about 19 to about 23 at
a transferred toner mass per area of about 0.35 to about 0.55
mg/cm.sup.2.
4. The developer according to claim 1, wherein the developer
provides a background of less than 100 particles/mm.sup.2.
5. The developer according to claim 1, wherein the toner particles
are emulsion aggregation toner particles.
6. A developer comprising black toner particles and carrier
particles, wherein the black toner particles comprise at least one
binder, at least one black colorant, and external additives,
wherein the at least one binder includes a styrene acrylate binder
including a cross-linked styrene acrylate gel content of from 0% to
about 12% by weight of the binder, wherein the external additives
include from about 1.3 to about 2.1% by weight of the toner
particles of a first silica having an average particle size of from
about 35 to about 45 nm, from about 0.5 to about 1.0% by weight of
the toner particles of a second silica having an average particle
size of from about 135 to about 160 nm, and from about 0.2 to about
0.5% by weight of the toner particles of a titania having an
average particle size of from about 35 to about 45 nm, and wherein
the external additives have a toner surface area coverage of from
about 25 to about 45%.
7. The developer according to claim 6, wherein the toner particles
comprise from about 7 to about 15 pph by weight of the
developer.
8. The developer according to claim 6, wherein the carrier
particles comprise a core of ferrite coated with a coating
comprising a polymethyl methacrylate polymer or copolymer, a
fluorine-containing polymer or copolymer, carbon black and melamine
beads.
9. The developer according to claim 8, wherein the coating
comprises from about 73 to about 77% by weight of the coating of
the polymethyl methacrylate polymer or copolymer, from about 5 to
about 7% by weight of the coating of the fluorine-containing
polymer or copolymer, from about 8 to about 10% by weight of the
coating of the carbon black and from about 9 to about 11% by weight
of the coating of the melamine beads.
10. The developer according to claim 8, wherein the coating is
present in an amount of about 0.6 to about 1.0% by weight of the
carrier.
11. The developer according to claim 6, wherein the cross-linked
styrene acrylate gel content of the toner particles is from 6% to
about 12% by weight of the binder.
12. The developer according to claim 6, wherein the styrene
acrylate binder of the toner particles is comprised of a copolymer
of styrene, n-butyl acrylate and .beta.-carboxyethyl acrylate.
13. The developer according to claim 12, wherein the copolymer is
derived from about 70 to about 90% by weight styrene, about 10 to
about 30% by weight n-butyl acrylate and about 0.5 to about 10 pph
by weight of the binder of .beta.-carboxyethyl acrylate.
14. The developer according to claim 6, wherein the at least one
black colorant includes carbon black.
15. The developer according to claim 6, wherein the second silica
is a sol-gel silica.
16. The developer according to claim 6, wherein the toner particles
further comprise from about 5 to about 15% by weight of the toner
particles of a wax.
17. The developer according to claim 6, wherein the toner particles
have an average particle size of from about 4 to about 7 .mu.m.
18. The developer according to claim 6, wherein the carrier
particles have an average diameter of from about 30 to about 55
.mu.m.
19. An electrophotographic image forming apparatus comprising a
photoreceptor, a semiconductive magnetic brush development system,
and a housing in association with the semiconductive magnetic brush
development system, wherein the housing delivers to the
semiconductive magnetic brush development system a developer
comprising black toner particles and carrier particles, wherein the
black toner particles comprise at least one binder, at least one
black colorant and one or more external additives, wherein the
toner particles comprise from about 7 to about 15 pph by weight of
the developer, and wherein the toner particles exhibit a
triboelectric charge of from about -25 to about -50 .mu.C/g at
toner particle concentrations of about 7 to about 15 pph by weight
of the developer.
Description
BACKGROUND
Described herein are black toners, developers containing the black
toners, and a method of forming images with the developers,
preferably utilizing a semiconductive magnetic brush development
system. More in particular, described herein are black toners
having specific properties and/or compositions such that the toner,
following triboelectric contact with a carrier, exhibits a
triboelectric charge of from about -25 to about -50 .mu.C/g so as
to provide a black toner image of superior image quality when used
to develop electrostatic images, particularly in a semiconductive
magnetic brush development system.
U.S. Pat. No. 5,545,501 describes an electrostatographic developer
composition comprising carrier particles and toner particles with a
toner particle size distribution having a volume average particle
size (t) (such that 4 .mu.m.ltoreq.t.ltoreq.12 .mu.m and an average
charge (absolute value) per diameter in femtocoulomb/10 .mu.m
(C.sub.T) after triboelectric contact with said carrier particles
such that 1 fc/10 .mu.m.ltoreq.C.sub.T.ltoreq.10 fc/10 .mu.m
characterized in that (i) said carrier particles have a saturation
magnetization value, M.sub.sat, expressed in Tesla (T) such that
M.sub.sat.gtoreq.0.30 T, (ii) said carrier particles have a volume
average particle size (C.sub.avg) such that 30
.mu.m.ltoreq.C.sub.avg.ltoreq.60 .mu.m, (iii) said volume based
particle size distribution of said carrier particles has at least
90% of the particles having a particle diameter C such that 0.5
C.sub.avg.ltoreq.C.ltoreq.2 C.sub.avg, (iv) said volume based
particles size distribution of said carrier particles comprises
less than b % particles smaller than 25 .mu.m wherein
b=0.35.times.(M.sub.sat).sup.2.times.P with M.sub.sat=saturation
magnetization value, M.sub.sat, expressed in T and P=the maximal
field strength of the magnetic developing pole expressed in kA/m,
and (v) said carrier particles comprise a core particle coated with
a resin coating in an amount (RC) such that 0.2% w/w.ltoreq.RC
.ltoreq.2% w/w. See the Abstract. This patent describes that such
developer achieves images of offset-quality in systems in which a
latent image is developed with a fine hair magnetic brush. See
column 4, lines 7-17 of the patent.
U.S. Pat. No. 6,319,647 describes a toner of toner particles
containing at least one binder, at least one colorant, and
preferably one or more external additives that is advantageously
formed into a developer and used in a magnetic brush development
system to achieve consistent, high quality copy images. The toner
particles, following triboelectric contact with carrier particles,
exhibit a charge per particle diameter (Q/D) of from 0.6 to 0.9
fC/.mu.m and a triboelectric charge of from 20 to 25 .mu.C/g. The
toner particles preferably have an average particle diameter of
from 7.8 to 8.3 microns. The toner is combined with carrier
particles to achieve a developer, the carrier particles preferably
having an average diameter of from 45 to 55 microns and including a
core of ferrite substantially free of copper and zinc coated with a
coating comprising a polyvinylidenefluoride polymer or copolymer
and a polymethyl methacrylate polymer or copolymer.
U.S. Pat. No. 6,361,915 describes a process for manufacturing a
conductive micropowder and includes the steps of: (i) forming an
aqueous dispersion of conductive material and the first surfactant,
(ii) mixing a latex emulsion of a polymer and a second surfactant
into the aqueous dispersion to form a suspension and (iii)
recovering the conductive micropowder from the suspension. The
first and second surfactants are of the same class and polarity.
The conductive micropowder finds particular utility as a coating
for carrier core particles, and as a conductive coating component
of carrier particle coatings.
U.S. Pat. No. 6,416,916 describes a toner of toner particles
containing at least one binder, at least one colorant, and an
external additive package comprised of zinc stearate and at least
one of silicon dioxide or titanium dioxide, wherein the amount of
zinc stearate is limited to about 0.10 percent by weight or less of
the toner. It is reported that when the amount of zinc stearate is
so limited, a developer formed from the toner exhibits excellent
triboelectric charging and stability and excellent developer flow.
When the developer is used in a magnetic brush development system,
consistent, high quality copy images are formed substantially
without any depletion defects over time.
What is still desired is a black toner for use in semiconductive
magnetic brush development systems, which toner is able to develop
a large number of pages per minute having high image density with
substantially reduced emissions and high print quality.
SUMMARY
In embodiments, described are developers comprised of toner
particles of at least one binder, at least one black colorant and
one or more external additives, together with carrier particles,
wherein the toner particles comprise from about 7 to about 15 pph
of the developer, and wherein the toner particles exhibit a
triboelectric charge of from about -25 to about -50 .mu.C/g at
toner particle concentrations of about 7 to about 15 pph of the
developer.
In embodiments, the toner particles include from about 6 to about
10% by weight of the black colorant, and the developer provides a
solid area image density of from about 19 to about 23 at a
transferred toner mass per area of about 0.35 to about 0.55
mg/cm.sup.2.
In embodiments, the black toner particles comprise at least one
binder, at least one black colorant, and external additives,
wherein the at least one binder includes a styrene acrylate binder
including a cross-linked styrene acrylate gel content of from 0% to
about 12% by weight of the binder, wherein the external additives
include from about 1.3 to about 2.1% by weight of the toner
particles of a first silica having an average particle size of from
about 35 to about 45 nm, from about 0.5 to about 1.0% by weight of
the toner particles of a second silica having an average particle
size of from about 135 to about 160 nm, and from about 0.2 to about
0.5% by weight of the toner particles of a titania having an
average particle size of from about 35 to about 45 nm, and wherein
the external additives have a toner surface area coverage of from
about 25 to about 45%.
In further embodiments, the styrene acrylate binder is comprised of
a copolymer of styrene, n-butyl acrylate and .beta.-carboxyethyl
acrylate, preferably of from about 70 to about 90% by weight
styrene, about 10 to about 30% by weight n-butyl acrylate and about
0.5 to about 10 pph of the binder of .beta.-carboxyethyl
acrylate.
In still further embodiments, the carrier particles of the
developer comprise a core, preferably of ferrite, coated with a
coating comprising a polymethyl methacrylate polymer or copolymer,
fluorine-containing polymer or copolymer, carbon black and melamine
beads, preferably including about 73 to about 77% by weight of the
coating of the polymethyl methacrylate polymer or copolymer, about
5 to about 7% by weight of the fluorine-containing polymer or
copolymer, about 8 to about 10% by weight carbon black and about 9
to about 11% by weight of the melamine beads. Preferably the
polymethyl methacryate polymer or copolymer is prepared as a latex
using sodium lauryl sulfate (SLS) as the surfactant in the latex
preparation step, followed by drying of the latex prior to coating
the carrier core. Preferably, the coating is present in an amount
of about 0.6 to about 1.0% by weight of the carrier.
In still further embodiments, described is an electrophotographic
image forming apparatus comprising a photoreceptor, a
semiconductive magnetic brush development system, and a housing in
association with the semiconductive magnetic brush development
system for containing the developers described herein.
DETAILED DESCRIPTION OF EMBODIMENTS
Generally, the process of electrophotographic printing includes
charging a photoconductive member to a substantially uniform
potential to sensitize the surface thereof. The charged portion of
the photoconductive surface is exposed to a light image from, for
example, a scanning laser beam, an LED source, etc., and of an
original document being reproduced. This records an electrostatic
latent image on the photoconductive surface of a photoreceptor.
After the electrostatic latent image is recorded on the
photoconductive surface, the latent image is developed with a toner
or developer containing a toner.
A two-component developer is used herein for development. A typical
two-component developer comprises magnetic carrier particles with
toner particles triboelectrically attracted thereto. During
development of the latent image, the toner particles are attracted
to the latent image, forming a toner powder image on the
photoconductive surface. The toner powder image is subsequently
transferred to an image transfer medium, e.g., a sheet of paper or
a transparency, either directly or via an intermediate transfer
member. Finally, the toner powder image is heated to permanently
fuse it to the image transfer medium.
A commonly known way of developing the latent image on the
photoreceptor is by use of one or more magnetic brushes. See, for
example, U.S. Pat. Nos. 5,416,566, 5,345,298, 4,465,730, 4,155,329
and 3,981,272, incorporated herein by reference. The toner of the
developer may be formulated to carry either a negative or positive
charge, and is in any case selected vis-a-vis the carrier so that
the toner particles acquire the proper operating charge with
respect to the latent electrostatic image being developed. Thus,
when the developer is brought into operative contact with the
photoconductive surface of the photoreceptor, the greater
attractive force of the discharged image causes the toner particles
to leave the carrier particles and adhere to the image portion of
the photoconductive surface.
The previously mentioned magnetic brush typically is comprised of a
roll having a tube-like member or sleeve, which is rotatably
supported. The sleeve is preferably made from a non-magnetic
material, more preferably stainless steel, which is conductive and
allows less eddy currents than aluminum so that localized heating
is reduced. One or more magnets are mounted inside the sleeve. The
roll is disposed so that a portion of the sleeve is immersed in or
in contact with a supply of developer comprising the carrier
particles and the toner particles.
As a result, the developer is made to be attracted to the surface
of the sleeve and arranges thereupon in the form of a brush, e.g.,
as bristles of a brush. Thus, when the photoreceptor bearing the
latent electrostatic image thereon is brought into physical contact
with the brush, the attractive force of the electrostatic charge on
the photoreceptor surface in the image areas, which is greater than
the force holding the toner particles is association with the
brush, draws the toner particles from the magnetic brush roller and
onto the image areas to render the image visible.
The electrophotographic marking process given above is ideal for
single color images, i.e., conventional black toner images. In such
process, the toner particles are colored black by way of a black
colorant included in the toner particles.
Described herein are novel developers including black toner that
operate in the restrictive semiconductive magnetic brush
development environment to achieve image qualities superior to
prior art toners and developers with the capability of forming a
large number of prints per minute (e.g., 100 or more prints per
minute) with reduced emissions and excellent background
performance. As a result of the reduced emissions with the toner,
solid and halftone areas are uniform and stable in density and
color, and text is crisp with well-defined edges regardless of font
size or type. In addition, background toner in non-image areas is
reduced, in particular to less than 100 particles per mm.sup.2,
preferably less than 50 particles per mm.sup.2, and machine dirt
and contamination is minimized.
In embodiments, the developer comprises black toner particles and
carrier particles, wherein the black toner particles comprise at
least one binder, at least one black colorant and one or more
external additives, wherein the toner particles comprise from about
7 to about 15 pph of the developer, and wherein the toner particles
exhibit a triboelectric charge of from about -25 to about -50
.mu.C/g at toner particle concentrations of about 7 to about 15 pph
of the developer.
This triboelectric charging versus toner concentration has been
found to permit the preferred high speed semiconductive magnetic
brush development system to operate with the aforementioned minimal
background and substantially no dirt or contamination. Moreover,
the developer is able to provide a solid area image density of from
about 19 to about 23 at a transferred toner mass per area of about
0.35 to about 0.55 mg/cm.sup.2. Solid area image density as
described herein is measured with a Gretag Macbeth reflection
spectrodensitometer or other suitable and/or similar device. It has
further been found that in achieving the aforementioned developer
properties, it is desirable that the toner particles include from
about 6 to about 10% by weight of the black colorant, most
preferably carbon black. The minimum black colorant loading of
about 6% by weight of the toner has been found necessary in
embodiments in order to achieve the desired solid image area
density, and the maximum loading amount of about 10% by weight of
the toner black colorant has been found necessary in embodiments to
limit the background to acceptable levels.
The black toner is preferably comprised of at least one resin
binder, at least one black colorant and an external additive
package comprised of one or more particulate additives. Suitable
and preferred materials for use in preparing the black toner are
discussed below.
In the black toner, the resin binder of the toner particles is
preferably comprised of an acrylate binder, more preferably a
styrene acrylate binder, most preferably of an emulsion aggregation
styrene acrylate binder.
If an emulsion aggregation styrene acrylate binder is used, such
may be prepared by any suitable emulsion aggregation process. As
one example, reference is made to U.S. Pat. No. 6,120,967,
incorporated herein by reference in its entirety. Emulsion
aggregation is a chemical process of forming the toner particles,
wherein the toner particles are built up from an emulsion of the
toner particle materials. Such a chemical process is generally
preferred over conventional physical processes that require
grinding and sizing to achieve the desired toner particle size and
size distribution.
In embodiments, the styrene acrylate binder of the toner particles
is comprised of a copolymer of at least styrene, n-butyl acrylate
and .beta.-carboxyethyl acrylate. Preferably, the copolymer is
derived from about 70 to about 90% by weight of the copolymer of
styrene, about 10 to about 30% by weight n-butyl acrylate and about
0.5 to about 10 pph of the binder of .beta.-carboxyethyl acrylate,
and more preferably about 15 to 25% by weight n-butyl acrylate and
about 1 to about 6 pph of the binder of .beta.-carboxyethyl
acrylate.
The styrene acrylate binder may be made to include some amount of
cross-linked gel portions therein. These cross-linked gel portions
are comprised of cross-linked binder distributed as microgel
particles throughout the linear portions of the binder. Such
cross-linked gel portions have a volume average particle size of
from, for example, 0.1 .mu.m or less, preferably about 0.005 to
about 0.1 .mu.m, as determined by scanning electron microscopy
and/or transmission electron microscopy.
The binder resin preferably has a weight fraction of the microgel
(cross-linked gel portion content) in the range from 0 to about 15%
by weight of the binder, preferably from about 0 to about 12% by
weight of the binder, more preferably from about 6 to about 12% by
weight of the binder. The linear portion is comprised of base
resin, preferably styrene acrylate, in the range from about 50 to
about 100% by weight of the binder, and preferably in the range
from about 65 to about 100% by weight of the binder. The linear
portion of the binder resin preferably comprises low molecular
weight reactive base resin that did not cross-link during a
cross-linking reaction. The molecular weight distribution of the
styrene acrylate binder resin is thus bimodal, having different
ranges for the linear and the cross-linked portions of the binder
resin.
The binder may also include some amount of additional binder
materials such as comprised of, for example, vinyl polymers such as
styrene polymers, acrylonitrile polymers, vinyl ether polymers,
acrylate and methacrylate polymers; epoxy polymers; diolefins;
polyurethanes; polyamides and polyimides; polyesters such as the
polymeric esterification products of a dicarboxylic acid and a diol
comprising a diphenol, crosslinked polyesters; and the like.
The binder of the toner particles is melt blended or otherwise
mixed with at least one black colorant. Various black colorants may
be used without limitation, and the colorant may be a pigment, dye
or mixture thereof. Example black colorants include, for example,
carbon black such as REGAL 330 carbon black (Cabot), acetylene
black, lamp black, aniline black and mixtures thereof. Most
preferably, the colorant is a carbon black pigment having a
suitable particle size such as, for example, about 50 to about 250
nm, and may be in the form of a dispersion, for example an aqueous
dispersion.
The black colorant is preferably included in the toner composition
in an amount of from about 1% to about 25% by weight of the toner
particles, preferably from about 5% to about 15% by weight of the
toner particles, most preferably from about 6 to about 10% by
weight of the toner particles, as discussed above.
The toner particles may also include several additional optional
additives within the toner particles (e.g., internal additives).
For example, as required, the toner particles may also include
charge control additives, surfactants, emulsifiers, pigment
dispersants, flow additives, and the like.
A wax, such as polyethylene, polypropylene, and/or paraffin wax, is
also preferably included in or on the toner composition as a fusing
release agent. In embodiments, the wax is included in the toner
particles in an amount of from about 5 to about 15% by weight of
the toner particles.
The toner particles of the present invention preferably have a
small size. In particular, the toner particles preferably have an
average particle size of from about 3 .mu.m to about 10 .mu.m,
preferably from about 4 .mu.m to about 7 .mu.m, most preferably
from about 5 .mu.m to about 6 .mu.m.
The toner particles also have one or more external additives on the
surface of the toner particles.
Preferably, the external additives comprise at least a first silica
having an average particle size of from about 35 to about 45 nm, a
second silica having an average particle size of from about 135 to
about 160 nm, and a titania having an average particle size of from
about 35 to about 45 nm.
The first silica (also known as SiO.sub.2 or silicon dioxide) is
preferably present in the toner particles in an amount of from
about 1.0 to about 3.0% by weight of the toner particles,
preferably from about 1.3 to about 2.1% by weight of the toner
particles. This first silica particle preferably has an average
particle size of about 40 nm. In general, silica is applied to the
toner surface for toner flow, triboelectric enhancement, admix
control, improved development and transfer stability and higher
toner blocking temperature. It has been found that the
aforementioned amounts of the sized first silica in the toner
particles can increase the toner particles triboelectric charge in
use and can also increase the charge per particle diameter (q/d) of
the toner in use. Silica particles of the aforementioned size range
are commercially available, for example from Nippon Aerosil Co.,
(NAC), Tokyo, Japan.
The second silica is preferably present in the toner particles in
an amount of from about 0.2 to about 2.0% by weight of the toner
particles, preferably from about 0.5 to about 1.0% by weight of the
toner particles. This second silica particle preferably has an
average particle size of about 140 nm to about 150 nm. It has been
found that this second silica may increase the cohesion of the
toner particles, but not to an extent that is unacceptable within
the aforementioned amount ranges. The second silica does not
negatively affect the triboelectric charging or q/d properties of
the toner particles.
The presence of these ultra large size second silica particles is
desirable in order to prevent impaction of the smaller sized
external additives into the toner particles during use of the
toner. During use, carrier particles knock into the toner
particles, and such impacts can force smaller external additives to
become undesirably impacted into the surface of the toner
particles. The larger sized second silica particles absorb the
impacts, and are of a sufficiently large size themselves to be less
susceptible to complete impaction into the toner particles. The
presence of the second silica particles thus ensures maintained
development and transfer performance of the toner over time.
The second silica particles are preferably sol-gel silica
particles. The second silica particles are commercially available,
for example from Shin-Etsu.
The titania particles (also known as TiO.sub.2 or titanium dioxide)
is preferably present in the toner particles in an amount of from
about 0.1 to about 1.0% by weight of the toner particles,
preferably from about 0.2 to about 0.5% by weight of the toner
particles. This titania particles preferably have an average
particle size of about 40 nm. In general, titania is added to the
surface of the toner particles for improved relative humidity (RH)
stability, triboelectric control and improved development and
transfer stability. Titania particles of the aforementioned size
range are commercially available, for example from Tayca.
Optionally, a third silica may be present in the toner particles in
an amount of from about 0.2 to about 5.0% by weight of the toner
particles. This third silica particle preferably has an average
particle size of about 8 nm to about 20 nm. The third silica may
contribute to improved charging and flowability. Example suitable
silicas in the size range of 8 nm to 20 nm and are commercially
available from Degussa and Cabot Corporation.
The external additives preferably are provided on the surface of
the toner particles in an amount such that the external additives
have a toner surface area coverage (SAC) of from about 25 to about
95%, preferably at least about 25 to about 45%. Developer life can
increase with higher SAC for high printing systems.
Additional external surface additives may also be included in the
external surface additive package. For example, the external
additive package may also include ZnSt (zinc stearate). Zinc
stearate provides lubricating properties, provides developer
conductivity and triboelectric enhancement, both due to its
lubricating nature, and can enable higher toner charge and charge
stability by increasing the number of contacts between toner and
carrier particles. Calcium stearate and magnesium stearate may also
be added to provide similar functions. A suitable commercially
available zinc stearate is known as Zinc Stearate L made by Ferro
Corporation, Polymer Additives Division.
The aforementioned external additives may be rendered hydrophobic,
if necessary, by surface treatments to reduce the humidity
sensitivity of the toner charging. The first silica and titania,
for example, may be treated with PDMS (polydimethyl siloxane). The
second silica may be treated with, for example, an organic
lane.
The following Table 1 sets forth several preferred toner
compositions, in which in Examples 1-8 preferred upper and lower
limits of the external additives are used and in Example 9 a middle
value for each component is used. All amounts are percentages by
weight, based on the total weight of the toner particles.
TABLE-US-00001 TABLE 1 Example First small size silica Second large
size silica Titania 1 1.37 0.59 0.30 2 2.05 0.59 0.30 3 1.37 0.89
0.30 4 2.05 0.89 0.30 5 1.37 0.59 0.44 6 2.05 0.59 0.44 7 1.37 0.89
0.44 8 2.05 0.89 0.44 9 1.71 0.74 0.37
The toner composition can be prepared by a number of known methods,
for example including physical methods such as melt blending the
toner resin particles, colorants and optional internal additives
followed by mechanical attrition. The toner may be made by first
mixing the binder, preferably comprised of both the linear resin
and the cross-linked resin as discussed above, and the colorant,
along with optional additives including a wax, together in a mixing
device. The toner is than classified to form a toner with the
desired volume median particle size. Care should be taken in the
method in order to limit the coarse particles, grits and giant
particles. Subsequent toner blending of the external additives is
preferably accomplished using a mixer or blender, for example a
Henschel mixer, followed by screening to obtain the final toner
product.
Other methods include those well known in the art such as spray
drying, melt dispersion, dispersion polymerization, suspension
polymerization, emulsion aggregation and extrusion. In embodiments,
the toner particles are preferably formed via a chemical method, in
particular emulsion aggregation. For example, such a process may
include at least forming a latex dispersion of the toner binder
materials, preparing a pigment dispersion, blending the latex
dispersion with the pigment dispersion, and optionally a wax
dispersion, to form a resin-pigment blend, adding a coagulant to
the resin-pigment blend, while continuously subjecting the mixture
to high shear, preferably with heating below a glass transition
temperature (Tg) of the resin binder, to form aggregate particles,
and heating the aggregate particles at temperatures above the Tg of
the binder resin, optionally with reduction of the pH, to form
coalesced toner particles.
Following formation via emulsion aggegation, the toner particles
may optionally be washed with an acid, e.g., calcium chloride. Such
acid washing can improve the relative humidity sensitivity of the
toner particles but can also lower triboelectric charging values of
the toner particles. Water washing, which does not substantially
affect the toner particle properties, may alternatively be
used.
The charge of a toner is described in terms of the charge/particle
diameter, q/d, in fC/.mu.m following triboelectric contact of the
toner with carrier particles. The charge per particle diameter
(q/d) of the toner particles preferably has an average value of
from, for example, -0.1 to -1.5 fC/.mu.m. This charge should remain
stable throughout the development process in order to insure
consistency in the richness of the images obtained using the toner.
The measurement of the average q/d of the toner particles can be
done by means of a charge spectrograph apparatus as well known in
the art. See, for example, U.S. Pat. No. 4,375,673, incorporated
herein by reference. The spectrograph is used to measure the
distribution of the toner particle charge (q in fC) with respect to
a measured toner diameter (d in .mu.m).
In a most preferred embodiment of the present invention, the toner
particles exhibit a triboelectric value (as measured by the known
blowoff process using a Faraday Cage), after triboelectric contact
with carrier particles, of from, for example, about -25 to about
-50 .mu.C/g, as measured in 70.degree. F. and 50% relative
humidity, as well as exhibits triboelectric stability over the life
of the developer.
The toner is most preferably incorporated into a two component
developer composition as discussed above by mixing with appropriate
carrier particles.
Suitable and preferred materials for use as carriers used in
preparing developers containing the above-discussed toners that
possess the properties discussed above will now be discussed. The
toner particles triboelectrically associate and/or adhere to the
surface of the carrier particles.
Illustrative examples of carrier particles that can be selected for
mixing with the toner composition prepared in accordance with the
present invention include those particles that are capable of
triboelectrically obtaining a charge of opposite polarity to that
of the toner particles. Illustrative examples of suitable carrier
particles include granular zircon, granular silicon, glass, steel,
nickel, ferrites, iron ferrites, silicon dioxide, and the like.
Other suitable carriers are disclosed in U.S. Pat. Nos. 4,937,166
and 4,935,326, the disclosures of which are hereby totally
incorporated by reference.
In a preferred embodiment, the carrier core is comprised of ferrite
particles. Any commercially available ferrite carrier may be used
without restriction. Preferably, the carrier core may be comprised
of a manganese magnesium ferrite core, such as commercially
available from Powder Tech. The ferrite particles to be used as
carrier cores in the developer composition preferably have an
average particle size (diameter) of from, for example, 10 to 100
.mu.m, preferably 20 to 70 .mu.m, most preferably 25 to 40 .mu.m,
as determined by standard laser diffraction techniques.
The selected carrier particles can be used with or without a
coating. In a preferred embodiment of the developer composition,
the carrier particles are coated with a polymethyl methacrylate
polymer or copolymer.
In another preferred embodiment, the ferrite carrier particles are
coated with a mixture of at least two dry polymer components, which
dry polymer components are preferably not in close proximity
thereto in the triboelectric series, and most preferably of
opposite charging polarities with respect to the toner selected.
The electronegative polymer, i.e., the polymer that will generally
impart a negative charge on the toner with which it is contacted,
is preferably comprised of a fluorine-containing polymer or
copolymer, e.g., polyvinylidenefluoride polymer or copolymer. Such
polyvinylidenefluoride polymers are commercially available, for
example under the tradename KYNAR. The electropositive polymer,
i.e., the polymer that will generally impart a negative charge on
the toner with which it is contacted, is preferably comprised of a
polymer or copolymer of polymethyl methacrylate (PMMA), optionally
having carbon black or another conductive material dispersed
therein. PMMA by itself is an insulative polymer. To obtain a
conductive carrier coating, a conductive component, for example
carbon black, is dry blended with the PMMA and any other carrier
coating constituents. The mixture is then tumbled onto the core and
fused.
The PMMA may be copolymerized with any desired comonomer, so long
as the resulting copolymer retains a suitable particle size.
Suitable comonomers can include monoalkyl, or dialkyl amines, such
as a dimethylaminoethyl methacrylate, diethylaminoethyl
methacrylate, diisopropylaminoethyl methacrylate, t-butylaminoethyl
methacrylate, and the like. If the PMMA polymer has carbon black
dispersed therein, it is preferably formed in a semisuspension
polymerization process, for example as described in U.S. Pat. No.
5,236,629, incorporated by reference herein in its entirety.
In a preferred embodiment of the invention, the carrier is coated
with a PMMA coating such as described in U.S. Pat. No. 5,847,030,
incorporated herein by reference in its entirety. Preferably, such
PMMA is made by an emulsion polymerization process and has a narrow
particle size distribution with polymer particles in the 100 to 200
nm size range, preferably about 150 nm. This small size is
desirable to provide uniform coverage on the small ferrite core. It
is further preferred that the polymethyl methacrylate prepared by
emulsion polymerization is prepared in the presence of sodium
lauryl sulphate surfactant to form the latex.
The percentage of each polymer present in the carrier coating can
vary depending on the specific components selected, the coating
weight and the properties desired. For example, the ratios of the
two polymers may be varied in order to adjust the triboelectric
characteristics of the carrier in order to meet the particular
requirements of a given printing device. Generally, the coated
polymer mixtures used contain from about 3 to about 97 percent of
the electronegative polymer, and from about 97 to about 3 percent
by weight of the electropositive polymer. Preferably, there are
selected mixtures of polymers with from about 3 to 25 percent by
weight of the electronegative polymer, and from about 97 to 75
percent by weight of the electropositive polymer. Most preferably,
there are selected mixtures of polymers with from about 5 to 15
percent by weight of the electronegative polymer, and from about 95
to 85 percent by weight of the electropositive polymer.
In a most preferred embodiment, the coating on the carrier
particles includes from about 70 to about 80% by weight, preferably
about 73 to about 77% by weight, of a polymethyl methacrylate
polymer or copolymer, from about 6 to about 12% by weight,
preferably about 8 to about 10% by weight, of carbon black, from
about 8 to about 12% by weight, preferably from about 9 to about
11% by weight, of melamine beads, and from about 3 to about 10% by
weight, preferably about 5 to about 7% by weight, of a
fluorine-containing polymer or copolymer.
As noted above, the coating on the ferrite carrier particles
preferably also includes melamine beads, for example melamine beads
having an average particles size of from about 100 nm to about 300
nm. Such beads are commercially available from, for example, Nippon
Shokubai. The melamine beads may comprise of from about 5 to about
15% by weight of the total coating, more preferably from about 8 to
about 12% by weight of the total coating. The melamine beads may
provide charging and conductivity stability.
The carrier particles may be prepared by mixing the carrier core
with from, for example, between about 0.05 to about 10 percent by
weight, most preferably between about 0.3 percent and about 5.0
percent by weight, based on the weight of the coated carrier
particles, of the coating composition until adherence thereof to
the carrier core by mechanical impaction and/or electrostatic
attraction. The mixture of carrier core particles and polymers is
then heated to an elevated temperature for a period of time
sufficient to melt and fuse to the coating polymers to the carrier
core particles. The coated carrier particles are then cooled and
thereafter classified to a desired particle size. The coating
preferably has a coating weight of from, for example, 0.1 to 5.0%
by weight of the carrier, preferably 0.6 to 1.0% by weight.
Various effective suitable methods can be used to apply the polymer
mixture coatings to the surface of the carrier core particles.
Examples of typical methods for this purpose include combining the
carrier core material and the coating composition by cascade roll
mixing, or tumbling, milling, shaking, electrostatic powder cloud
spraying, fluidized bed, electrostatic disc processing, and an
electrostatic curtain.
The coated carrier particles preferably have a size of from about
25 .mu.m to about 40 .mu.m, more preferably of about 35 .mu.m. In a
preferred embodiment, it is desirable to maintain a ratio of
carrier volume median diameter to toner volume median diameter of
approximately 5:1 to 9:1.
Two component developer compositions of the present invention can
be generated by mixing the carrier core particles with the toner
composition discussed above. The carrier particles can be mixed
with the toner particles in various suitable combinations. However,
best results are obtained when from about 1 part to about 25 parts
by weight of the black toner and from about 75 parts to about 99
parts by weight of the carrier particles, are mixed. Preferably,
the toner concentration in the developer is from about 7 to about
15 pph of the developer. The toner concentration in the developer
initially installed in a xerographic development housing is thus
preferably between, for example, about 7 to about 15% by weight
based on the total developer weight.
The developers of the invention exhibit superior black image
quality, reduced emissions, and enable the device to print a large
number of pages per minute (ppm), for example on the order of 100
to 200 ppm or more, without quality problems arising.
To determine the tribo, a 0.5 gram sample of developer is placed in
a Faraday cage. Pressurized air is blown through the cage that has
screens at each end. The screen size allows toner to escape and
retains carrier. A 15 micron screen is best for 35 micron carrier
and 5.5 micron toner. An electrometer is attached to the cage and
monitors charge change as toner exits the cage. The weight change
is measured from before to after blowoff and toner mass is
obtained. Tribo is defined as toner charge/toner mass.
Developability may fall off if toner surface additives move to the
carrier, if the surface additives get impacted into the toner and
or if the developer conductivity drops.
The measured background for each of the Example toners 1-9 above is
very low, and is below about 50 particles per mm.sup.2. Background
is measured by picking up untransferred toner off the photoreceptor
with adhesive tape and counting the number of toner particles per
square millimeter.
While the subject matter has been described in conjunction with
specific embodiments described above, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, the embodiments, as set
forth above, are intended to be illustrative and not limiting.
Various changes may be made without departing from the spirit and
scope of the subject matter described herein.
* * * * *